Antenna Trimming - Cutting

[anf_r5]

For a mobile antenna cut and tuned to approximately 172Mhz, should I expect any noticeable degradation in performance Rx and Tx on 150-160 Mhz?
At 172Mhz, the antenna is about 2.5" shorter than necessary for 150-160Mhz.

The antenna in question is a Laird B132 VHF 1/4 wave.

Thanks

 

[mmckenna]

Maybe a bit, but unlikely you'd hear the difference unless you were on the very fringes of coverage.

If you had enough whip, you could tune it between the two (161MHz) and it would give pretty good performance across the 150-170MHz range.

 

[prcguy]

I agree the degradation will be minimal but you can get wide band 1/4 wave whips that will cover your entire range with a good match. They usually stick a fat tapered spring at the base to help increase band width.

 

[anf_r5]

Maybe a bit, but unlikely you'd hear the difference unless you were on the very fringes of coverage.

Interesting. That is what I've been experiencing. On the fringes, 150-160 Rx and Tx is scratchy and unreadable using the antenna tuned to 172.

On another radio with a multiband antenna that covers 130-170, the same frequencies in the same location come in scratchy but still readable.

I also know there might be variance in the radios. I plan to swap antennas as an experiment and see how that goes.

 

[mmckenna]

On another radio with a multiband antenna that covers 130-170, the same frequencies in the same location come in scratchy but still readable.

Those multiband antennas are usually tuned to favor the middle of the VHF band. If you look at the sweep of a multiband antenna, or even a quarter wave antenna, you'll see a nice smooth sweep across the band. SWR/reflected power gets worse out towards the very edges.

Swapping antennas might result in the issue following the antenna.
Since 1/4 wave antennas are pretty dang cheap, just buy a new one and tune it down around 160MHz.

Here's the VHF sweep from an EM Wave multiband antenna:


Note that it's lowest SWR is right at 161MHz. Even out at the bottom of the 2 meter ham band and up at 174MHz, it's still under 1.7:1 SWR.

Here's the sweep from a Larsen NMOWBQ Wide Band Quarter wave (like PRCGUY was suggesting). This one was on my personal truck and I cut it for around 156MHz, which was in the middle of my work VHF stuff (but still worked fine on the 2 meter ham band);